1. Field of the Invention
This invention relates to a parallel folding apparatus of a folding machine, which can smoothly perform transfer of a signature between a first jaw cylinder and a second jaw cylinder during parallel folding.
2. Description of the Related Art
A web rotary printing press is equipped with a folding machine for cutting a web, which has been dried and cooled after printing, into predetermined lengths, and folding the cut web in a width direction or a lengthwise direction.
The folding machine is available with various structures and, for example, is equipped with a parallel folding apparatus as shown in FIG. 4 or FIG. 5 (see Japanese Patent Application Laid-Open No. 2000-95431; hereinafter referred to as Patent Document 1).
The parallel folding apparatus has a cut-off cylinder 1, a folding cylinder 2, a first jaw cylinder 3, and a second jaw cylinder 4 opposed to one another in contact with one another and rotating in directions of arrows in FIG. 4. A web 8, which has been fed between nipping rollers 5→cross perforation cylinders 6→nipping rollers 7, is cut to predetermined dimensions by a cut-off knife (not shown) of the cut-off cylinder 1. The front end of the cut web is transported by a pin (not shown) of the folding cylinder 2, and then the cut web is parallel-folded between a single folding knife (not shown) of the folding cylinder 2 and a site between a gripper board 10 and a gripper jaw 11 of the first jaw cylinder 3 to form a signature 9. In the case of a single parallel fold, the signature 9 is transported, unchanged, toward a chopper 14 by a gripper 12 and a gripper pad 13 of the second jaw cylinder 4. In the case of a double parallel fold or a delta fold, the signature 9 is further parallel-folded between a double folding knife (not shown) of the first jaw cylinder 3 and a site between a gripper board 15 and a gripper jaw 16 of the second jaw cylinder 4 to form a double parallel fold. The so folded signature 9 is transported toward the chopper 14.
In FIG. 5, 17a to 17c denote signature transport/holding brushes used in the transfer of the signature 9 between the first jaw cylinder 3 and the second jaw cylinder 4. Instead of these signature transport/holding brushes 17a to 17c, a continuous guide plate 18 may conventionally be provided to provide along the circumferential surface of the first jaw cylinder 3 and the circumferential surface of the second jaw cylinder 4, as shown in FIG. 6.
In providing the continuous guide plate 18 along the circumferential surface of the first jaw cylinder 3 and the circumferential surface of the second jaw cylinder 4 in a folding machine as described in patent document 1, it has been conventional practice to provide the guide plate 18 stationarily (although its initial position can be adjusted) with respect to a stay bar 19 extending between frames.
To have a double parallel fold or a delta fold, the front end of the signature 9 gripped between the gripper board 10 and the gripper jaw 11 (see FIG. 4) of the first jaw cylinder 3 is released at a predetermined time point (the time point before the folded portion of the signature 9 is gripped, for gripping change, between the double folding knife of the first jaw cylinder 3 and the site between the gripper board 15 and the gripper jaw 16 of the second jaw cylinder 4) after passing through the point of contact between the first jaw cylinder 3 and the second jaw cylinder 4. During a low speed operation of the folding machine (during acceleration at the start of operation, or during speed reduction at completion of operation), the following problem may occur at the time of release: That is, the front end of the signature 9 is not guided into a clearance between the guide plate 18 and the circumferential surface of the first jaw cylinder 3, but enters a space between the guide plate 18 and the circumferential surface of the second jaw cylinder 4. As a result, the trouble may occur that the signature 9 is folded up in a curled state, or dropped without being folded up, whereby a jam is caused. That is, during a low speed operation, the front end of the signature 9 is not guided into the clearance between the guide plate 18 and the circumferential surface of the first jaw cylinder 3, but enters the space between the guide plate 18 and the second jaw cylinder 4, because of weak inertia. Consequently, the signature 9 is not guided by the guide plate and the circumferential surface of the first jaw cylinder. In other words, during a high speed operation (during a routine constant speed operation), the front end of the signature 9 is positively guided into the clearance between the guide plate 18 and the circumferential surface of the first jaw cylinder 3 by means of inertia, so that there is no problem. If the guide plate is located toward the site of contact between the first jaw cylinder and the second jaw cylinder, on the other hand, the front end of the signature 9 is guided by the guide plate during a low speed operation, but the trouble arises that the signature is rubbed by the guide plate during a high speed operation. Even in the case of the signature transport/holding brushes 17a to 17c, the brushes 17a to 17c wear and become unable to guide the signature, presenting the same problems as those caused by the guide plate 18.